Strain relief



Jan. 17, 1950 C H 2,494,814

STRAIN RELIEF Filed May 31, 1946 3 Sheets-Sheet l jive/Zion Car! 4 7/7551 Jan. 17,1950- I c. M. HUTH 2,494,814

STRA IN RELiEF Filed May :51, 1946 s Sheets-Sheet 2 Jan. 17, 1950 c. M. HUTH 2,494,814

STRAIN RELIEF Filed May 31, 1946 I SSheets-Sheet 3 ezzzaz' 6/2221 f? 175% AM Q11 i Patented Jan. 17, 1950 LCarlIMIH'u'th,Richmond, Ind, assignor to Bel'den ManufacturingCompany,v Chicago; 'Ill.,='a corporation of'lllinois Application May-=31, 194 6,wScrial No.67,3,584

'15 Claims. 1

The present invention relates .to-strainirlieis,

and ,particularly---to bushing-type strain reliefs :adaptedafor userin connection with. electrical conv.ductorcords.

-.Strain ireliefs are @widely utilized to prevent .damage to ztheselectrical connections between conductor cords and the appliances or. other electrical-apparatus with -which such cords-.are Custornarily employed. .wIn-its simplest formgthe usual strain relief comprises-can enlargement,

such .as .a. sleeve or bushing, which mechanically engages thezcord, usually-the device is bonded to the :insulation disposed on "the outside of l'the cord conductors, and means forv mechanically connectin thestrain:relieftothe'irame orsome other portion of .the structure of the associated apparatus. Bushing-type strainreliefs are particularly desirable,v due .to ,their -.low cost .and

ease'of manufacture, but thebushing-type strain 'zreliefs heretofore. known in =the art.,-have not proven entirely :satisfactory. -.While the cost-of "the known devices iiS.10 \V,'. .thBy: are inherently rather 'dimcultvtoixassemble into ;the associated apparatus, unless that lapparatus :includes.-.a

multipart means :for receiving :th strain'reliei and once the known devices are zassembledwthey are very 'difficult'to disassemble.

The present invention, :therefore,..is i'concerned with the provision-of an-improved bushing type strain relief, andhasfor its principal. object, the provision of an improved bushing-type strain relief which s'hallbe'much'easierto attach-to the "structure of the'asso'ciated apparatus; and which shall be capable-ormuch more convenient disassemblyywh'en des'iredfthanthe-known devices of this general type. As will hereinafter appear, this object isha'ccomplishedby the-"provisionoi 'a' bushing-typehttain relief wh'ich is -so con- .structed that one end thereofi'may b readily inserted into an opening gprovidedfin the associated. apparatus, whereupon rotation "of "the strain. relief will cause it .to engage the associated apparatus witha strain-resisting engagement. Thedevice. may lthus tbe assemblecinmore .easily than the priorart.structures,.since very little-force is .requiredito put. 'thestrain relief into, place, andhit .is likewise. .susceptible, of

equally [convenient disassembly. .The I various ,-features and advantages of the .invention :willbe.

'made more apparent in the accompanyingdrawings and the-following description .ofcertaimper- 'fected'embodiments thereof.

In the drawings,

'lie'f,..in accordance with the invention, applied .to a two-conductor,."electrical conductor cord;

.:Fig..2-, is a plan .view ofithe strain relief shown inFigil;

.iFigs. 3, .4 and .5 are perspective views showing themanner in which the strain relief illustratted'inFigs '1 and 2 is put. into use;

Figs. 6 and .7 are, respectively, side elevation ,and plan views of a second illustrative embodi- ,ment.- of the strain relief of the invention;

Fig. 8 is a perspective view of the 'strain relief vshown in Figs. 6 and '7. The view'showsithe strain. relief cut away along the general line .8-'8-of Fig. 6, and theparts have been angularly, displaced to clarify the showing;

.Iliig. 9., isa sectional view on the line 9'9 of .Fig.-'6;

, Rig. ;10;is.,a.side elevational view of a ,third i1- .lustrative embodiment of the invention;

Figs, 11-, and 12 ,are views-showing two steps in .theassemblvof the strain relief shown in Fig.10;

YEig'ZlBv isahside elevation viewoi another embodiment .ofithe invention and (Figs. 1-14 and 15 are views similar to Figs. 11

and 12, showing ,the assembly of the Fig. '13 em- .bodiment.

The strain relief .means'illustrated in Figs. 1

'..tof.5is of the bushing or sleeve type, and inaCllldBS two main body portions 2| and 23, which .are securely.attachedtothe conductor cord 25 .with'whichthe device is used. The body por- .,tion 2 l of..the strain vrelieitapers in the direction of: theouter end thereofland has an inner end ;.ment portion i 29 of uniform thickness. .,abutment portion. 29v is.'also oval in cross sec- .45.

v or abutmentportion 21 which is of substantially uniform thickness.longitudinally, of the bushing. .The.=ablu'tment..portion 21 has the crosssectional. outline of a slightly flattened circle, or oval,.as is. shown particularly in Fig; 3.

. The .kbody .portion.-',23..of the strain relief also :tapers'in thedirection oflthe outer end thereof, and also .termin'atesin anoinner end or abut- The ...tionjbutthe ovalis much narrower and the cross. sectional. area is muchlessthanithe cross-sectionalarea. of "the abutment portion 21. The

-.major. axis .of.,the narrower abutment portion 2931s rotated ,90..rela'tive to the major. axis of the otherabutment portion 121, as shown. The

. two. main body .portionsIZl and -23 .of thestrain (relief are ,partially separated .from, each other bywan intermuralaspace 3|, which has the gen- :131'31 form of. .aninterrupted, annular. groove, and Fig. .1 1 is a side .elevational View -of. a1strain ,re+:-,55

which. defines opposed, spaced-apart, para1lel,

3 abutment surfaces at the inner ends of the abutment portions 21 and 29.

The face of the abutment portion 27 is provided with an integral boss or projection 33 which is of substantially the same form and cross-sectional area as the abutment portion 29. The boss or projection 33 is disposed with its major axis rotated 90 from the major axis of the oval-shaped, abutment portion 29. As will hereinafter appear, the boss or projection 33 is employed to prevent axial rotation of the strain relief bushing when the end surfaces of the abutments 21 and 29 are in strain relieving engagement with the associated apparatus.

The strain relief can be most conveniently manufactured by molding it directly onto the cord with which it is to be used, and to make possible the attainment of all of the advantages of the invention, at least part of the strain relief should be of a resilient, yieldable material. Moldable rubber compounds similar in composition to those commonly used for molding the bodies of electrical connector plugs, electrical insulation and the like are suitable for this purpose. While the particular conductor cord illustrated at in the various figures of the draWings is of the two-conductor type and is provided with a molded-on rubber insulation, it will be understood that the strain reliefs of the invention are suitable for use with almost any type of conductor cord.

The frame, or some other portion of the structure of the apparatus with which the strain relief device is to be used, is provided with an opening which is most conveniently of substantially the same outline as one of the abutment portions, and that opening is adapted to receive one of the main body portions of the device during the assembly operation. The exact manner in which the particular strain relief illustrated in Figs. 1 and 2 is put into use is shown particularly in Figs. 3, 4 and 5. In these figures, a portion of the frame or other structure of th associated apparatus, which might be the chassis of a radio set, is illustrated .at 35. The frame structure is provided with an oval opening 31 of suitable form and dimension to receive freely the body portion 23, including the oval-shaped abutment portion 29 of the strain relief, and during assembly, the body portion 23 is pushed entirely through the opening 31 to the position shown in Fig. 4. When in this position, the entire strain relief is rotated 90 to bring the parts into the position shown in Fig. 5, which is the normal operating position of the device. In this position, the oval abutment portion 29 is at right angles to the oval opening 31 provided for receiving the strain relief, and the oval-shaped boss or projection 33 on the inner face of the other abutment portion 21 of the strain relief snaps into, and is seated within, the opening 31, so as to resist turning of the strain relief.

Desirably the width of the intermural space 3| provided between the abutment surfaces is slightly less than the thickness of the plate or other structural element with which the strain relief coacts. This provides a good snug engagement of the parts and aids in holding the strain relief in place. Depending upon requirements, the intermural space 3| can be made as narrow as desired, with increasing tightness of engagement between the end wall surfaces of the strain relief and the support therefore, due to the longitudinal displacement of the resilient material of which the strain relief is made. In an extreme case, as where the strain relief is used with a thin, sheet metal, frame member, the intermural space may constitute simply a cut separating the abutment surfaces.

It will be apparent that when the strain relief is in the strain resisting position, there is a very considerable body of material in the abutments 21 and 29 which is available to transmit any strain which may be placed on the cord to the structure of the apparatus with which the cord and strain relief are used. Stressing of the electrical connections to the cord conductors is thereby effectively prevented. At the same time, should it be desired to remove the cord for repair or service, this may be readily done by rotating the strain relief so as to bring the narrower body portion 23 and the abutment 29 into aligmnent with the opening 31 in the frame or other cooperating structure. In this position the strain relief and cord may be freely disengaged from the associated apparatus.

Some yielding and relative movement between the component parts of the strain relief bushing is required during either the installation or removal in order to seat and unseat the locking boss or projection 33. However, the force required to effect this is relatively small, and in practical sizes of the device, using ordinary molding compounds, may be readily applied by a slight twist of the hand.

The embodiment of the invention illustrated in Figs. 6 through 9 is, in general, similar to the embodiment just described. This device includes a pair of opposed, outwardly tapering, body portions 39 and 4| having abutment sections 43 and 45, which are generally oval in cross section and which are separated by an intermural space 41 so as to provide opposed, spaced-apart, abutment surfaces for engaging the wall structure of the apparatus with which the device is used. Similar to the previously-described strain relief, the abutment end of the body portion 4| is somewhat narrower in cross section and has a somewhat smaller cross-sectional area than the abutment which constitutes a part of the body portion 39. This facilitates easy assembly of the device and improves the appearance of the assembled unit. Also, in this embodiment, the inner face of the larger abutment 43 is provided with a boss or looking projection 49, having substantially the same cross-sectional outline and area as the narrower abutment 45 of the device.

There is however, one important difference in this embodiment of the invention. The thickness of the boss or looking projection 49 is substantially less than the thickness of the intermural space 41 separating the abutting surfaces of the two opposed body portions 39 and 4| of the strain relief. As a result, the face of the narrower abutment 45 is connected to the boss or looking projection 49, and to the remainder of the device, through a molded section 5| which may be substantially circular in outline and which may have the same or a slightly smaller diameter than the width of the narrower body portion 4|, as shown particularly in Fig. 8. Decreasing the thickness of the locking projection 0r boss 49 facilitates the assembly of the device since it limits the amount of material which must be distorted when the strain relief is rotated into strain resisting position.

This construction is particularly useful when the strain relief engages a relatively thick structural section of the associated apparatus with accompanying increase in the width of the interamgcia mural space l1. when lthe construction "o'fthe "apparatus with- Which the cord and strain -relie'i are-to be usd is-such thatthe strain rlfe'f may engagea relatively thin metal plate, "which is the preferred arrangement, decreasing the thickopposed abutments -may ii take -various -shapes,

other th'an the broa'd an-d narrow ovals there illustrated. Thea'dvantages of the'inventionwill be bbtainedgat least in i part, in anyconstruction whereinabutment su'r'faces, *angula'rly disposed relat'ive to each oth'er,--can be obtained, and.1in generaL thisacondition willbe fulfilled bylthe use of -one abutment which is :of =non-circu1ar shape or outline. For 'example,--as shown-in: Figs 10, llyand 12;0ne"of the body portionsof the istrain "relief may be p'rovided'with a cylindrical end. or abutment section 53; and the ot-her body portion may have an-abutment section 55 which is he);-

agonal in shape, with 'a hexagonally shaped. locking projection- 51,rdisplaced 30 ffrom. :the hex- -a'gon'al abutment section .55, 'mechani'callyl 'conmeeting the two body: portions.

This. construction is adapted-to 'sfit a hexagonal openings59in the frame or:-'other structure -60 of the associated apparatus, as shown :in Fig. -11, and during. use :the body-:portionhavingthehexagonal abutment section '55 is slipped tthrough ithe opening 59 and is -then rotated 30f so as ito v effectiresilient, looking engagement of the hexagonal locking pro- ;jec'tion :51- with the opening :59. Z'This construction: does n'otma-ke availablesas much material'for strainresistance in a'direction-toward the circular abutment section 553, but'sincertain instances,:the constru'ction-may be desirable.

A somewhat different structural. sarrangement o'f the invention is illustrated imFigs. 11.3,: 14zand "15. This device includes'o'ppositelyzdisposed, outwardly :tapering body-:portionslfil :and 16 3,1similar 'ito thei previously':.described constructions. The wbody p ortionifi r isiprovided with :a .cylindricallys'hapedi abutment sectionefi5;and this is adapted to coactzwith:ianzabntmentisection 6:1 formediin- EtBEISJIYzWithLtIH-Z body-portionzfi3. T-hebody portion 63 and-theabutment 161 are oval in cross- *'section andhare' adapted to:-.fit within anoval opening; such.as thezopeningillustrated at 69, @provided-in agplate; section .or zotherlpart 1 Lof :the -struoturetof the apparatus with which .the cord nandtstrainrelief are used.

.The two abutment-sections andfil areseparated byanintermuralrspace or groove 12 which idefines-spacedeapart. abutment, surfaces, as in the previously-described embodimentsl "The'two body portions .6! and-5.3 am connected by acylindrical central section l3.having ,a diameter which desirably is ap roximately equal 'to, .or somewhatsmaller than,'the minor axis of the oval-shaped .ab'utme'ntB'l.

The locking means used for "lockingthe strain 'relief bushing against rotation when the abutment surfaces are "in strain relieving position; in "ithisin'stance, comprisestwo cylindrically shaped projections 15 having rounded'ends,which-'extend outward1y'from-one of theabutment surfaces and Whichare adapted to engage suitable circular when "the strainn'elief- "has been placed in lthe opening 15! :androtated to the- 1 strain resisting position" illustrated iri Fig. 15.

In this*-*eons'trution,' as the previously described embo'dimentspf the invention, the provision of lockinglmeans for preventing rotation of 1 the strain r'elief when it is in operative position, makes it necessary that the component parts of the bushing shall be constructed of material which permits yielding and relative movement betweenthe parts whenth'e-bushing is being rotatedinto the---s'train=resisting position. Otherwise, it would n'ot' be possible to effect seating -o'f thelocking-meansJ 'Itismost convenient, ashas -been previously indicated, to manufacturethe entirestrainrelief bushing in one'piece of a re- *silient, yieldable' materi'al,*such as one of the *moldable rubber compounds used-for electrical insulating purposes. Wherrmade in this manner the bushingmaybeunoldddirectly onto *the as- "sociated' coi'd 25*and"will be securely attached thereto as an incidentof the molding operation. "In a" constructionsuch as is illustrated in Figs. l 3j=14-and 15-bitmay-be desirable to' utilize look- *ing pro-j ections which are of a somewhat harder 'material'thantheusual-molding compound. "Itis desirablefiin this construction; that the length of the a locking proj e'ctions-"or -boss'es- "shall be less "than the width of 'the' interrnural space which separates the opposed abutment surfaces, and this is espe'cially '-true-when the bosses or other locking "projectionsare made of a hard material. I It=-is= not "essential that the strain relief be 'molded -on, 'or'otherwise integrally "joined to; the associated conductor -'-c'ord. The dimensions of "'thestra'in relief maybe *such that it will tightly grip thecord with which it isto be used by virtue of itsownresilience. another alternative con- *str-uction; the dimensions and shape of the portion of' the-strain=relief which connects the two opposed abutment s-urfac'esmay -be so correlated with relation to the cooperatingopening in the strain reli'ef =suppcrt,- that the r'otative positioningof the strain relief in such opening will cause thesentral-rportion of the strain-relief to be compressed so as to -tightly engage the associated In the=foregoing there have been described the features-o'f certainillustrative embodiments of :zan improved "bushing -type strain relief which "is particularly adapted for use 1 in connection with ='el'e'ctrical conductor cords. 'As has been previously pointed outy strain reliefs in accordance ewith the presentdnventi'on may be assembled -=-with a minimum of eifort -and with very slight *d'eformation of -the component parts thereof. 'Eacho'f the devices provides for the provision or m'ea'ns ior ositively- 100m the strain relief in :operativeposition; yet-atthe same time, the natureof the locking means is such that the strain vr eIief may-be readilydisengaged from the asso- "ciated appar'atusat"any time. 'The invention,

- -therefore, obviates the defects and disadvantages "or" the -prior art'constructions. The broad concept of rotating a member of resilient construc- "non-circular --opening""formed therein, an 'eleo op 1 p ovi d n ithe n 'st c I *tricaiconducting eorarandabushing-type strain relief which is disposed about said cord and which is adapted to be received within said opening to provide a strain relief for said cord, said strain relief bushing being constructed at least in part of resilient material and having two main body portions which terminate in opposed, abutment surfaces which are separated by a narrow, intermural space, the shape and the cross-sectional dimensions of said body portions being such that at least one of said body portions can be inserted into the non-circular opening provided in said wall structure and, following such insertion, can be rotated to bring said abutment surfaces into strain resisting position, the width of said intermural space being less than the thickness of said wall structure in order that said surfaces shall resiliently engage said wall structure to prevent rotation of said strain relief bushing from the strain resisting position.

2. In combination, a plate member having a non-circular opening formed therein, an electrical conducting cord, and a bushing-type strain relief which is disposed about said cord and which is adapted to be received within said opening to provide a strain relief for said cord, said strain relief bushing being constructed at least in part of resilient material and having two main body portions which terminate in opposed, substantially parallel, abutment surfaces which are separated by a narrow, groove-like, intermural space, the shape and the cross-sectional dimensions of said body portions being such that at least one of said body portions can be inserted into the non-circular opening provided in said plate member and, following such insertion, can be rotated to bring said abutment surfaces into strain resisting position, the width of said intermural space being less than the thickness of said plate member in order that said surfaces shall resiliently engage said plate member to prevent rotation of said strain relief bushing from the strain resisting position.

3. In combination, a wall structure having a. non-circular opening formed therein, an electrical conducting cord, and a bushing-type strain relief which is disposed about said cord and which is adapted to be received within said opening to provide a strain relief for said cord, said strain relief bushing being constructed at least in part of resilient material and having two main body portions which terminate in opposed abutments, having end surfaces which are separated by a narrow, groove-like, intermural space, the crosssectional area of one of said abutments being substantially greater than th cross-sectional area of the opening provided in said wall structure, and the cross-sectional dimensions and area of the other abutment being substantially the same as the corresponding dimensions and area of said opening whereby one end of said bushing can be freely inserted in said opening and then rotated to bring said abutments into strain resisting position, the width of said intermural space being less than the thickness of said wall structure in order that said abutment surfaces shall resiliently engage said wall structure to prevent rotation of said bushing from the strain resisting position.

4. In combination a wall structure having a non-circular opening formed therein, an electrical conducting cord, and a bushing-type strain relief which is disposed about said cord and which is adapted to be received within said opening to provide a strain relief for said cord, said strain relief-bushing having two main body portions which terminate in opposed, abutment surfaces which are separated by a narrow, groove-like, intermural space, the shape and cross-sectional dimensions of said body portions being such that at least one of said body portions can be inserted into the non-circular opening provided in said wall structure and, following such insertion, can be rotated to bring said abutment surfaces into strain resisting position, the width of said intermural space being such that said abutment surfaces are at leastv in close proximity to the surfaces of said wall structure when said bushing is in strain resisting position, and means for resiliently locking said bushing in strain resisting position, said means comprising a boss or projection which projects from one of said abutment surfaces and which is adapted to engage and lock with said wall structure when said abutment surfaces are in strain resisting position, the component parts of said bushing being constructed of material which permits yielding and relative movement between said parts when said bushing is being rotated into strain resisting position.

5. In combination a wall structure having a non-circular opening formed therein, an electrical conducting cord, and a bushing-type strain relief which is disposed about said cord and which is adapted to be received within said opening to provide a strain relief for said cord, said strain relief bushing having two main body portions which terminate in opposed, abutment surfaces which are separated by a narrow, groove-like, intermural space, the shape and cross-sectional dimensions of said body portions being such that at least one of said body portions can be inserted into the non-circular opening provided in said wall structure and, following such insertion, can be rotated to bring said abutment surfaces into strain resisting position, the width of said intermural space being such that said abutment surfaces are at least in close proximity to the surfaces of said wall structure when said bushing is in strain resisting position, and means for resiliently locking said bushing in strain resisting position, said means comprising a boss or projection of resilient material which projects from one of said abutment surfaces and which is adapted to yield when said bushing is being rotated to strain resisting position and to engage and lock with the sides of the opening in said wall structure when said bushing is in strain resisting position.

6. In combination, a wall structure having a non-circular opening formed therein, an electrical conductor cord, and a bushing-type strain relief of resilient material which is attached to said cord and which is adapted to be received within said opening, said strain relief bushing having two, main body portions, which terminate in opposed, abutment surfaces, which are separated by a narrow, groove-like, intermural space, the shape and cross-sectional dimensions of said body portions being such that one of said body portions can be freely inserted into said noncircular opening and, following such insertion, can be rotated to bring said abutment surfaces into strain-resisting position, and means for resiliently holding said strain relief bushing against rotation when said abutment surfaces are in strain-resisting position, said means comprising at least one boss or projection which projects from one of said abutment surfaces and which is adapted to engage and resiliently lock with the sides of said non-circular opening when said surfaces are in strain-resisting position.

A QQ in; omb nat on arms; on-circular;.openingao msd ther nran electr c conductor cord, and a bushing-type strain relief which is attached;lto;.,-said;;1cordj; and which is adapted, tidy-he received-within said non-circular op nin sa d: strain-:relief ,abushing; two, main bodyportiens;.which, terminate-in opposed, abutment surfaces,whiohnrerseparated =by-;a;narrow, groove-like iintermural space; the cross-sectional area of one: of :said; ahutments being sub: stantially-greater; than theecrossesectional,a a of said non-circular; opening; theqcrossesectional dimensions: and area of: these her dryxnor ion being;,substantiailyathezsarne:a heecmlrespflnd ing dimensions. and ameasizeli#Sfiidi- T'QW UI Y ope in r by onexendsc .isaimbusmnearcan benfreel-y :insentedii-n SillihabPfiflilkg and zthfini 'fif' tated ;tobring saidgabutmentsinto :s,trai-n;-;resistins position, and means; resiliently docking said bushing; in" steam-resisting position, said means comprisingsat,ileast,:oneaboss :or P170160:- tion which extends? fromwonezof said abutmen surfaces. andYWhi'ch risieadaptndz toyengage' d lock with said plate member, at least a pantwf said bushing being- Constructsd ofzmaterialjwhich penmits yielding. and-:relatiwe; movement r between said main body; lportionspwhen-xsaid bushing is bfiingdfit'aziied' ll'ItQiStlfliIlFeSiSting7ipOSiti0Hl :8. In'combination, a lplatewmember havin a non-circular opening iormcd therein, an electrical conductor COX'd; andiazbushing -'tyrpe strain relief which isaattached;tee-saidacord' and which a n t he= received-within,:saidnon-circular openin g, :said: strain relies bushing; having; two,

main. body port-ionsv-whichsterminate zinc QDD G;

abutment surfaces; which are separated by a narrow, groove-like intermural space, the crosssectional area of one-of= said'abutments being substantially greater .thanthe cross-sectional area of said non-circular opening, the cross sectional dimensions and area of the other body portion beingsubstantially the sameas the corresponding dimensions and area of said non-circular opening, whereby onesendzof said:bushine can be :freely inserted in suchiopening, ,andthen rotated to' bring said abutments'into strain -resisting position, the width of said intermural space being such that said abutment surfaces are at least in close proximity to the surfaces of said plate member when said bushing is in strainresisting position, and means for resiliently looking said bushing in strain resisting position, said means comprising at least one boss or projection which extends from the surface of the abutment of greater area, which has the same general outline and cross sectional dimensions as said noncircular opening, and which is disposed with its maior axis at an angle to the major cross sectional axis of said abutment of lesser area, said boss or projection being adapted to engage and lock with the sides of said non-circular opening in said plate member when said bushing is in strain-resisting position and said bushing being constructed of resilient material which permits yielding and relative movement between said main body portions when said bushing is being rotated into strain-resisting position.

9. In combination, a wall structure having a non-circular opening formed therein, an electrical conducting cord, and a bushing type strain relief which is disposed about and is attached to said cord and which is adapted to be received within said opening, said strain relief bushing having two main body portions which terminate in opposed abutment surfaces which are separated byla narrow grooveelike, .intermural space, the shape and cross sectional dimensions ofv I said body portions being-,such that at least-oneof saidlbody portions can-be-freely inserted into said non-circular:opening and, following. such insertion, can be rotatedwtobringsaiduabutment surfaces into strain resisting position, the width of said interniural;-space being suchthat said abutment.surfaceseare at:least in closeproximity to the surface of said, wall structurewhen said bushing is in strainresisting position, and means for preventing rotationof said strain relief -bushing'when said.abutment surfa-ces are in strain resisting position, said means comprising a boss or projection which: extends from one; of said abutment surfaces and whichis adaptedto engage lock withsaid--wallstructu-re, the component parts. of said, bushing-being constructed ofmaterial which permits yieldingand relative movement between saidinain bod-y-pprtions-when said bushing is being rotated-into strain resisting position; and the-thickness of said boss or projectionbeingsubstantially less thanthe width of the intermuralspace which existssbetweenssaid spaced apart abutment 1 surface.

10-. In combination, a'zplatamember havinga non-circular opening formed therein; an electrical conductor cord, anda; bushing, type strainrelief which is disposed-about, and is attached to, said cord and; which isadapted to isereceived within said non-circular opening, saidv strainrelief bushing having two maintbcdy-portions which terminater-inrropposed, substantiallygparallei, abutment surfaces whichraresseparated by; a narrow, groove-like.intermural space; the-cross sectional area Dione-of sa-id-abutments being substantially greatenthan thercros-s sectional area of said nonecircularepening ;the crosssseotional dimensions and area mi the other. body portionbeing substantially; the-same ,as the corresponding dimensionsuande area'of said non-circular opening, whereby one end ofsaid bushing can be-freely inserted into the non-circular opening provided in said platel-m-ernber and, following suchinsertion, can ,be rotated to. :bringsaid abutment. surfaces intmstrain ,iresisting position, the width of said intermural space being such that said abutment surfaces are at least in close proximity to the surfaces of said plate member when said bushing is in strain-resisting position, and means for resiliently locking said bushing strain resisting position, said means comprising at least one boss or projection which extends from the surface of the abutment of greater area, which has the same general outline and cross sectional dimensions as said non-circular opening, and which is disposed with its major cross sectional axis at an angle to the major cross sectional axis of said abutment of lesser area, said boss or projection being adapted to engage and lock with the sides of said non-circular opening in said plate member when said bushing is in strain resisting position and being of a substantially less thickness than the width of said intermural space, said bushing being constructed of resilient material which permits yielding and relative movement between said main body portions when said bushing is being rotated into the strain resisting position.

11. In combination, an electrical conductor cord, and a bushing type strain relief which is disposed about, and is attached to, said cord, said strain relief bushing being constructed at least in part of resilient material, and having two main body portions which terminate in opposed abutments having substantially parallel abutment surfaces, which are separated by a narrow, groovelike, intermural space, one of said abutments being non-circular in outline, the other of said abutments being generally circular in outline and having a diameter which is at least substantially as great as the major cross sectional axis of the abutment which is non-circular in outline, and a boss or projection which extends into said intermural space from the surface of the abutment which is circular in outline, said boss or projection haVil'ig the same general outline and crosssectional dimensions as said non-circular abutment and being disposed with its major axis at an angle to the major cross sectional axis of said non-circular abutment.

12. In combination, an electrical conductor cord, and a bushing type strain relief which is disposed about said cord, said strain relief bushing being constructed at least in part of resilient material and having two main body portions which terminate in opposed abutments, said abutments having substantially parallel abutment surfaces, said surfaces being separated by a narrow groove-like intermural space, and a noncircular boss or projection which projects from one of said abutment surfaces into said intermural space, and at least a substantial portion of the other of said abutment surfaces being in superpositioned, overlying relation with respect to a substantial portion of said non-circular abutment surface.

13. In combination, an electrical conductor cord, and a bushing type strain relief which is disposed about, and is attached to, said cord, said strain relief bushing being constructed at least in part of resilient material, and having two main body portions which terminate in opposed abutments, said abutments having substantially parallel abutment surfaces and said surfaces being separated by a narrow, groove-like, intermural space, and a non-circular boss positioned within said intermural space so as to interconnect said abutment surfaces, at least one of said abutments being non-circular in outline and the other of said abutment surfaces having a substantial portion thereof in superpositioned, overlying relation with respect to said non-circular abutment surface.

14. In combination, an electrical conductor cord, and a bushing type strain relief which is disposed about, and is attached to said cord, said strain relief bushing being constructed at least in part of resilient material and having two main body portions which terminate in opposed abutments, said abutments having substantially parallel abutment surfaces, said surfaces being separated by a narrow groove-like intermural space, the area of one of said abutments being substantially greater than the area of the other of said abutments, the smaller of said abutment areas being non-circular in outline, and means comprising a boss or projection which extends from the surface of the abutment of greater area, said boss having substantially the same general outline and cross-sectional dimensions as said noncircular abutment surface, and being disposed with its major axis at an angle to the major cross-sectional axis of said abutment of lesser area.

15. In combination, an electrical conductor cord, and a bushing type strain relief which is disposed about said cord, said strain relief bushing being constructed at least in part of resilient material and having two main body portions which terminate in opposed abutments, said abutments having substantially parallel abutment surfaces, said surfaces being separated by a narrow groove-like intermural space, and a non-circular boss or projection which projects from one of said abutment surfaces into said intermural space.

' CARL M. HUTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,094,990 Havens Apr. 28, 1914 2,115,495 Mapelsden Apr. 26, 1938 2,165,952 Alsrom July 11, 1939 

